The protonation equilibria of selected glycine dipeptides in ethanol–water mixture: solvent composition effect

Abstract

Knowledge of the protonation constants of small dipeptide is important, interesting and necessary for complete understanding of the physiochemical behavior of dipeptide. In this study, the protonation constants of some aliphatic dipeptides (Gly-Gly, Gly-Val, Gly-Leu, Gly-Thr, Gly-Phe and Gly-Met) were studied in water and ethanol-water mixtures [20% ethanol-80% water, 40% ethanol-60% water, 60% ethanol-40% water, (v/v)] at 25 +/- 0.1 degrees C under nitrogen atmosphere and ionic strength at 0.10 mol dm(-3) by potentiometry. The constants of the systems were calculated by using BEST computer program, and distribution species diagrams were produced using the SPE computer program. The protonation constants were influenced by changes in solvent composition, and their variations were discussed in terms of solvent and structural properties. The concentration distribution of the various species in ethanol-water mixtures was evaluated.

The multiple roles of histidine in protein interactions

“…Figure 3 shows the repulsive cation-π interactions between the protonated histidine (His + ) and cations as the function of distance R. In protein structures the histidine frequently and reversibly transforms from neutral form to protonated form [6,59,60]. Based on our calculations the proton transformation in His may switch the cation-π interactions from attractive to repulsive.…”

“…The unique structure of histidine makes it plays multiple roles in the molecular interactions. The roles of histidine in molecular interactions are even complicated by pH condition and its two protonation forms, the neutral form and the protonated form [6]. Figure 1 shows the optimized structures of histidine in the neutral form ( A ) and in the protonated form ( B ).…”

Protonation Equilibria of Biologically Active Ligands in Mixed Aqueous Organic Solvents

“…For this purpose, by examining the protonation equilibria of dipeptides with solvent composition, it is generally observed that log⁡ 10 ⁡ K 1 values decrease with the increase in the mole fraction of ethanol, whereas log⁡ 10 ⁡ K 2 values increase as the composition of ethanol increases in water-ethanol mixture. The decrease in log⁡ 10 ⁡ K 1 values and increase in log⁡ 10 ⁡ K 2 values of all dipeptides with the increasing ethanol concentration were the same as for the corresponding free amino acids [48]. …”

Evaluation of protonation constants of glycylglycine in acetonitrile– and ethylene glycol–water mixtures

“…They are components of tissues [1] exhibiting a remarkable range of biological properties acting as antibiotics, hormones, food additives, poisons, or painkillers. [2] Investigations involving the peptides in acid-base reactions [3,4] particularly, small peptides have attracted great attention in relation to the bioinorganic chemistry because these compounds are usually considered as good model systems to attain a better insight into the characteristics of naturally occurring metalloproteins.…”